Novel prepregs

Abstract

A prepreg comprising a porous support material impregnated with a binder consisting essentially of an epoxy resin, a bisphenol novolac hardener and 0.4 to 2.0% by weight based on the total binder of an imidazole and a method of preparing laminates of composite materials therefrom.

What I claim is: 
     
       1. A prepreg comprising a porous support material impregnated with a binder consisting essentially of an epoxy resin, 5 to 40% by weight of a bisphenol novolac hardener based on the total binder weight and 0.4 to 2.0% by weight based on total binder of an imidazole. 
     
     
       2. A prepreg of claim 1 containing 0.7 to 1.0% by weight of an imidazole. 
     
     
       3. A prepreg of claim 1 wherein the bisphenol for the novolac hardener has the formula ##STR2## wherein R 1  and R 2  are individually lower alkyl of 1 to 4 carbon atoms. 
     
     
       4. A prepreg of claim 1 wherein the imidazole is selected for the group consisting of imidazole, 2-phenyl-imidazole, 2-methyl-imidazole, 1-methyl-imidazole and 2-ethyl-4-methyl-imidazole and their reaction products with ethylene oxide, propylene oxide or acetonitrile. 
     
     
       5. A method for the continuous production of composite materials based on epoxy resin laminates by heating prepregs in a heated dual belt press, the improvement comprising using as the prepreg a prepreg of claim 1. 
     
     
       6. The method of claim 5 wherein the binder contains 0.7 to 1% by weight of an imidazole. 
     
     
       7. The method of claim 5 wherein the binder contains 5 to 40% by weight % of bisphenol-based novolac. 
     
     
       8. The method of claim 5 wherein the continuous laminate production occurs at temperatures of 170° to 230° C. 
     
     
       9. The method of claim 8 wherein the temperature is 190° to 220° C. 
     
     
       10. A composite material circuit board prepared from a laminate product by the process of claim 5.